The present invention is directed to a method, an apparatus and a calibration substrate for calibrating a travel path and/or an angular position of a holding device in a means for manufacturing electrical assemblies, particularly for equipping printed circuit boards with components.
For calibration of a travel path and/or of an angular position of a holding device in a means for manufacturing electrical assemblies, for example, a calibration substrate of a printed circuit board was previously equipped with simulations of the components at defined placement locations. The simulations are conveyed at the holding device to a calibration substrate from a magazine, analogous to the transport of components from delivery units up to the placement location on a printed circuit board. It is standard to employ a glass plate similar to a printed circuit board as the calibration substrate, and has centering marks in its corner regions. The glass plate is provided with a double-sided adhesive film or with a spray glue and is placed into a means, for example an automatic equipping unit, whereupon the position of the centering marks is identified with a topically resolving printed circuit board camera of the automatic equipping unit. Subsequently, the calibration substrate is equipped with simulations of components at locations defined relative to the centering marks.
The equipped glass plate can then be measured in various ways. In a first known method, the equipped glass plate is placed into an optical measuring instrument. The glass laminae exhibit the fine markings whose position relative to the centering marks of the glass plate is determined in the measuring instrument. Correction values are determined from the positional deviations from the desired ideal position in the coordinate directions and with respect to the rotated amplitude. These are input as correction parameters into the automatic equipping machine that takes these deviations into consideration during the later equipping of printed circuit boards with components.
A further prior art method is disclosed in German Patent Application 197 11 476.8. Here, the equipped glass plate is measured in the automatic equipping unit by the printed circuit board camera. The printed circuit board camera thereby registers local reference marks in its field of view that are present on the glass plate, together with defined markings of the glass laminae. The corresponding correction values are determined from their relative positions, these correction values being subsequently taken into consideration when equipping printed circuit boards with components.
The printed circuit board camera, however, exhibits an individual-dependent camera distortion that is especially pronounced given lenses with a short focal length. Due to this situation, errors in the range of .+-.15 .mu.m arise when measuring automatic equipping units and what is thereby the multiple use of this optical sensor unit.